Field/frame conversion circuit

ABSTRACT

A field/frame conversion circuit for use in a magnetic recording/reproducing apparatus which magnetically records and reproduces still images or the like. 
     In the field/frame conversion circuit, after the frequency of a field signal obtained from a magnetic recording medium such as a magnetic disc and composed of frequency-multiplexed brightness and chroma signals is converted into a higher frequency band than the frequency band of the brightness signal, the field signal is delayed in the frequency modulated state thereof 0.5 horizontal scan period necessary for the field/frame conversion by a signal delay line having a wide band frequency characteristic. The thus delayed field signal and an undelayed field signal are selected alternately at every one vertical scan period by signal switching means so as to perform the field/frame conversion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a field/frame conversion circuit foruse in a magnetic recording/reproducing apparatus adapted to record andreproduce still images or the like and, in particular, to a field/frameconversion circuit in which, when a field signal reproduced from amagnetic recording medium is delayed one-half of a horizontal scanperiod in order to provide a frame signal, the field signal is delayedin a high frequency bandwidth.

2. Description of the Prior Art

In forming a television picture image, it is well known that ainterlaced scanning is employed in an horizontal scanning in order toreduce flicker to the eyes. In the NTSC system, this interlaced scanningis a [2 to 1] interlaced scanning method. In the [2 to 1] interlacedscanning method, a picture (that is, a frame) is structured bysuperposing two rough pictures (that is, two fields) on each other, eachof the fields being formed by means of one vertical scanning.Accordingly, the number of repetitions of the frames is 30 times persecond and the number of the field repetitions is 60 times per second.Also, odd fields and even fields are delayed from each other by 0.5 Hwhere 1 H represents a horizontal scanning period.

By the way, when recording video signals in a recording medium such as amagnetic tape, a magnetic disc or the like, various kinds of recordingmethods are conventionally employed. Among them, for example, there is amethod in which a video signal is divided into two signal components,that is, a brightness signal and a chroma signal, and the two dividedsignals are processed in a given manner and are then frequencymodulated, before they are recorded into the magnetic recording medium.

For reproduction in such recording method, there is employed a so-calledfield/frame conversion technique in which the strong verticalcorrelation of the video signal is used to scan the same recordedportion twice so that a frame signal can be created from one kind offield signal. In the field/frame conversion technique, since the fieldcan not be divided into the odd fields and even fields simply byrepeating the same field signal there are formed two kinds of signals,that is, a signal that is delayed 0.5 H from the field signal (0.5 Hdelay signal) and a signal that is not delayed (non-delay signal), andthese two kinds of signals are switched so as to provide the odd andeven fields.

In a field/frame conversion circuit to realize the above-mentionedfield/frame conversion system, a 0.5 H delay line is used to to providethe signal that is delayed 0.5 H from the field signal and a chargecoupled device (CCD) is employed in the 0.5 H delay line. The delay lineusing the CCD is not so good in S/N (signal-to-noise ratio) thefrequency characteristic thereof does not exhibit a wide bandwidth and,therefore, the brightness signal and the chroma signal must be convertedseparately into the frame signal. This requires two kinds of differentdelay lines (that is, glass delay line and CCD delay line) which aredifferent from each other in characteristic. The difference incharacteristic between the glass and CCD delay lines results in a greatdifference of delay time between the brightness and chroma signals whichcan produce color discrepancies.

Also, in the above-mentioned field/frame conversion circuit, when thechroma signal is demodulated, there is employed a bandwith which is notsuitable to demodulate the chroma signal, resulting in a distortedchroma signal.

It may be considered that, instead of the above-mentioned two differentkinds of delay lines, the one CCD delay line is used as the delay linefor the brightness and chroma signals and at least the brightness signalis delayed 0.5 H after it is demodulated.

However, in this case, there may be produced a slight level differencebetween the non-delay brightness signal and the 0.5 H-delayed brightnesssignal, which results in a flicker of 30 Hz. In order to prevent theproduction of such flicker, a complicated circuit configuration must beused.

SUMMARY OF THE INVENTION

The present invention aims at eliminating the drawbacks found in theabove-mentioned prior art systems.

Accordingly, it is an object of the invention to provide a field/frameconversion circuit which can prevent color discrepancies and flickerwhich may be caused by delaying a brightness signal and a chroma signal0.5 H separately using two different kinds of delay lines, and alsowhich allows a simplified circuit configuration.

In order to attain the above object, according to the invention, thereis provided a field/frame conversion circuit in which a non-delay signalwhich is a modulated field signal that is input repeatedly and which issupplied with no delay and a delay signal which is delayed 0.5 H(horizontal scanning period) are selected by switching means at eachvertical scanning period to thereby provide a frame signal,characterized in that said input modulated field signal is a modulatedfield signal that is composed of at least two signals modulated andfrequency multiplexed, and the 0.5 horizontal scanning period delay isperformed in a state in which the frequency of the repeatedly inputmodulated field signal is once converted into a higher frequency.

It is another object of the invention to improve the reproductioncharacteristic of the chroma signal.

In accomplishing this object, according to the invention, after themodulated field signal comprising the frequency multiplexed brightnesssignal and chroma signal is converted into a frame signal, the chromasignal component of the frame signal is extracted from the frame signal,or the chroma signal is extracted from the above-mentioned modulatedfield signal, and then the frequency of the thus-extracted chroma signalis converted into a given bandwidth before it is demodulated.

BRIEF DESCRIPTION OF THE DRAWINGS

The exact nature of this invention, as well as other objects andadvantages thereof, will be readily apparent from consideration of thefollowing specification relating to the accompanying drawings, in whichlike reference characters designate the same or similar parts throughoutthe figures thereof and wherein:

FIG. 1 is a block diagram of an embodiment of a reproducing system in amagnetic recording/reproducing apparatus to which the invention isapplied;

FIG. 2 is a block diagram of another embodiment of a reproducing systemin a magnetic recording/reproducing apparatus to which the invention isapplied;

FIG. 3 is a characteristic view to show the frequency characteristic andgroup delay characteristic of a 0.5 H delay line;

FIG. 4 is a block diagram of still another embodiment of a reproducingsystem in a magnetic recording/reproducing apparatus to which theinvention is applied;

FIG. 5 is a characteristic view to show the frequency characteristic ofa field signal employed in the embodiment shown in FIG. 4;

FIG. 6 is a block diagram of yet another embodiment of a reproducingsystem in a magnetic recording/reproducing apparatus to which theinvention is applied;

FIG. 7 is a characteristic view to show the frequency characteristic ofa field signal employed in the embodiment shown in FIG. 6;

FIG. 8 is a block diagram of a further embodiment of a reproducingsystem in a magnetic recording/reproducing apparatus to which theinvention is applied;

FIG. 9 is a circuit diagram to show a basic structure to realizefield/frame conversion;

FIG. 10 is a timing chart to show the operation state of a field/frameconverison switch employed in the circuit shown in FIG. 9;

FIG. 11 is a block diagram of a still further embodiment of areproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied;

FIG. 12 is a block diagram of a yet further embodiment of a reproducingsystem in a magnetic recording/reproducing apparatus to which theinvention is applied;

FIG. 13 is a block diagram to show a structure of a demodulation circuitemployed in the embodiment shown in FIGS. 11 and 12;

FIG. 14 is a block diagram of another embodiment of a reproducing systemin a magnetic recording/reproducing apparatus to which the inveniton isapplied; and,

FIG. 15 is a block diagram of a further embodiment of a reproducingsystem in a magnetic recording/reproducing apparatus to which theinvention is applied.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description will hereunder be given of the preferredembodiments of a circuit for converting a field signal into a framesignal according to the present invention with reference to theaccompanying drawings.

Referring first to FIG. 1, there is illustrated in block form astructure of a reproducing system of a magnetic recording/reproducingapparatus to which the present invention is applied. In FIG. 1, amagnetic head 10 is connected to the input terminal of an amplifier 11and the output terminal of the amplifier 11 is connected to the inputterminal of a first frequency converter 12, whereby a field signal thatis reproduced repeatedly by the magnetic head 10 is amplified by theamplifier 11 and is then supplied to the first frequency converter 12.

A signal having a given frequency f1 (for example, about 28 MHz)produced by in a local oscillator 13 is supplied to the first frequencyconverter 12, and in this first frequency converter 12 theabove-mentioned signal (frequency f1) is mixed with the field signal toobtain a sum or difference signal thereof.

The above-mentioned field signal is composed of a brightness signal witha frequency bandwidth fy and a chroma signal with a frequency bandwidthfc, and thus it has a bandwidth of fc+fy (for example, 0˜10 MHz). Thefirst frequency converter 12 outputs a signal having a frequency in ahigher bandwidth of fc+fy+f1 (for example, 28˜38 MHz) at the output ofthe circuit.

The output terminal of the first frequency converter 12 is connected toone contact a of a field/frame conversion switch 14 and is alsoconnected via a 0.5 H delay line 15 to the other contact b of thefield/frame conversion switch 14, so that the output signal (with afrequency of fc+fy+f1) of the first frequency converter 12 can beapplied to the one contact a of the field/frame conversion switch 14 aswell as to the other contact b of the field/frame conversion switch 14via delay line 15.

Here, as the 0.5 H delay line 15, there is used a glass delay line whichhas a wide bandwidth frequency characteristic. The frequencycharacteristic and group delay characteristic of the glass delay lineare shown in FIG. 3. In FIG. 3, it can be seen that a curved line Arepresents the frequency characteristic of the delay line and it has abandwidth of 16˜44 MHz. That is, since the frequency bandwidth of theoutput signal of the first frequency converter 12, as described above,is in the range of 28˜33 MHz, when the above-mentioned delay line isused, then there can be obtained a sufficient bandwidth, so that thefrequency characteristic of the glass delay line is satisfactory inpractical use.

Also, a curved line B represents the group delay characteristic of theglass delay line and the width of variation of the delay time in thebandwidth of 16˜44 MHz is within 100 n sec. The variation width of thedelay time may give rise to color discrepancies but such colordiscrepancies can be practically neglected.

The above-mentioned field/frame conversion switch 14 is an analog switchwhich is adapted to select alternately a non-delay field signal 16 and afield signal 17 from the 0.5 H delay line 15 at each vertical scanningperiod (1 V) in accordance with a control signal 18 to convert into aframe signal 19. Th output terminal of the field/frame conversion switch14 is connected to a second frequency converter 20, so that the framesignal 19 from the conversion switch 14 can be supplied to the secondfrequency converter 20.

The above-mentioned second frequency converter 20 is a circuit which isadapted to take in a signal with oscillation frequency f1 from the localoscillator 13, mix the signal (frequency f1) with a frame signal (withthe frequency of fc+fy+f1), and output a difference signal (withfrequency of fc+fy) between these two signals. The output terminal ofthe second frequency converter 20 is connected through a high-passfilter 21 to a brightness signal demodulation circuit 23, and is alsoconnected through a low-pass filter 22 to a chroma signal demodulationcircuit 26. The high-pass filter 21 is adapted to allow the brightnesssignal component (fy, for example, 2.5˜10 MHz) of the output signal(fc+fy, for example, 0˜10 MHz) output from the second frequencyconverter 20 to pass therethrough, so that the brightness signalcomponent can be demodulated by the brightness signal demodulationcircuit 23 into a brightness signal Y.

On the other hand, the low-pass filter 21 allows only the chroma signalcomponent (fc, for example, 0˜2.5 MHz) of the frame signal 19 to passtherethrough, so that the chroma signal component can be applied to thechroma signal demodulation circuit 26 where it can be demodulated into achroma signal.

Next, description will be given of the operation of theabove-constructed embodiment.

The field signal having the frequency bandwidth of fc+fy that isrepeatedly reproduced by the magnetic head 10 is first amplified by theamplifier 11 and is then supplied to the first frequency converter 12.The field signal supplied to the first frequency converter 12 is mixedwith a signal of a frequency f1 output from the local oscillator 13 andthe mixed signal is output from the first frequency converter 12 as asum signal component with a high frequency bandwidth (that is, afrequency of fc+fy+f1). The signal that is output from the firstfrequency converter 12 is divided into two signals; that is, a signal 16which is supplied undelayed the contact a of the field/frame conversionswitch 14; and, a signal 17 which is supplied through the 0.5 H delayline 15 to the other contact b of the switch 14. These two kinds ofsignals are selected alternately at each 1 V by the conversion switch 14and converted into the frame signal 19 which is in turn supplied to thesecond frequency converter 20.

The frame signal 19 supplied to the second frequency converter 20 ismixed here with a signal output from the local oscillator 13 and thus itis converted again into a signal with a low frequency bandwidth (fc+fy).When the signal with a frequency (fc+fy) is supplied to the high-passfilter 21, then only the brightness signal component (fy) of the signalcan be output from the high-pass filter 21. By applying the brightnesssignal component (fy) to the brightness signal demodulation circuit 23,the brightness signal Y can be obtained. Also, the signal with afrequency (fc+fy) is supplied to the low-pass filter 22, then only thechroma signal component (fc) is output from the low-pass filter 22. Byapplying the chroma signal component (fc) to the chroma signaldemodulation circuit 26, the chroma signal C can be obtained.

As described above, in this embodiment, a frequency modulated fieldsignal comprising a brightness signal component and a chroma signalcomponent both of which are frequency multiplexed in frequency is onceconverted into a signal which has a high frequency bandwidth, and thethus converted field signal is delayed only 0.5 H by a 0.5 H glass delayline which has a wide band frequency characteristic and a good groupdelay characteristic, before a frame signal is created. Therefore,according to the embodiment, a circuit configuration can be simplifiedand, since there is produced almost no difference in delay time betweenthe brightness and chroma signals, there is eliminated the possibilitythat color discrepancies may be produced in a reproduced image.

Also, according to the embodiment, since the delay of the brightness andchroma signals is carried out in the frequency modulated states thereofprior to demodulation, there is eliminated the possibility that flickermay be produced.

Further, the 0.5 H glass delay line employed in the embodiment providesless signal degradation when compared with a CCD and, therefore, it isbetter in S/N (a signal-to-noise ratio) than the CCD. Accordingly, inaccordance with the present embodiment, there can be obtained a framesignal which has a good S/N.

Referring next to FIG. 2, there is shown another embodiment of areproducing system employed in a magnetic recording/reproducingapparatus to which the invention is applied.

Also in this embodiment, the same parts thereof as in theabove-mentioned first embodiment are given the same reference charactersfor convenience of explanation.

The embodiment shown in FIG. 2 is different in structure from theembodiment in FIG. 1 in that it performs the field/frame conversion inlower frequencies (for example, 0˜10MHz), but the embodiment in FIG. 2is similar to the embodiment in FIG. 1 in that a field signal is delayed0.5 H in high frequency bandwith by use of a glass delay line having aside frequency bandwidth, which is the subject matter of the presentinvention. In other words, according to the circuit configuration of theembodiment shown in FIG. 2, a field signal with a frequency of fc+fywhich is repeatedly reproduced by the magnetic head 10 is amplified bythe amplifier 11 and the field signal is then divided into two signals:one being a signal 16A to be supplied intact to one contact a of thefield/frame conversion switch 14; and the other being a signal 17A whichis supplied to the other contact b of the conversion switch 14 after itis once converted by the first frequency converter 12 into a signal witha high frequency of fc+fy+f1 (for example, 28˜38 MHz), is delayed 0.5 H,and is then converted by the second frequency converter 20 to a signalwith its initial frequency of fc+fy (for example, 0˜10 MHz). The switch14 is adapted to select the above-mentioned signals 16A and 17Aalternately at each 1 V according to a control signal so as to obtain aframe signal 19A. The frame signal 19A which is obtained from the switch14 is then applied to a high-pass filter 21 and a low-pass filter 22.

The high-pass filter 21 is structured such that the output thereof issupplied to a brightness signal demodulation circuit 23.

The low-pass filter 22 is a circuit which permits to pass through onlythe chroma signal component with a frequency of fc (for example, 0˜2.5MHz) of the frame signal 19A. The chroma signal component that haspassed through the low-pass filter 22 is then applied to a chromademodulation circuit 26 to provide a chroma signal.

Description will be given below of the embodiment shown in FIG. 2.

The field signal that is reproduced repetitively by the magnetic head 10is first amplified by the amplifier 11 and it is then applied to the oneterminal a of the above-mentioned switch 14 as well as to the firstfrequency converter 12. The field signal that is applied to the firstfrequency converter 12 is once converted into a signal with a highfrequency of (fc+fy+f1) and is then supplied to a 0.5 H delay line 15.The field signal that is delayed only 0.5 H by the 0.5 H delay line 15is converted again by second frequency converter 20 to a signal with alow frequency of (fc+fy) and is then applied to the other contact b ofthe switch 14. The signal 16A to be applied to the one terminal a of theswitch 14 and the signal 17A to be applied to the other terminal bthereof can be selected alternately to provide the frame signal 19A.

The frame signal 19A is applied via the high-pass filter 21 to thebrightness signal demodulation circuit 23 to provide a brightness signalY.

Also, when the frame signal 19A is passed through the low-pass filter22, then only the chroma signal component (fc) threof is extractedtherefrom, and the chroma signal component (fc) is then applied to thechroma signal demodulation circuit 26 to provide a provide a chromasignal C.

The embodiment shown in FIG. 2 can provide several effects similar tothose of the before-mentioned embodiment shown in FIG. 1. In addition tothem, the present embodiment has a further effect that the circuitconfiguration thereof can be simplified since a switching operation forfield/frame conversion can be performed in a lower frequency band.

Referring next to FIG. 4, there is illustrated a third embodiment of areproducing system in a magnetic recording/reproducing apparatus S towhich the invention is applied.

In FIG. 4, reference character 30 designates a magnetic disc; 32 amagnetic head adapted to reproduce a field signal which is composed of afrequency modulated (FM) brightness signal Y (for example, with afrequency bandwidth fy=2.5˜12 MHz) and an FM chroma signal C (forexample, with a frequency bandwidth fc=0.15˜2.5 MHz) respectivelyrecorded on a track of the magnetic disc 30; 34 an amplifier adapted toamplify the field signal that is reproduced by the magnetic head 32; 36a first frequency conversion circuit adapted to convert the field signaloutput from the amplifier 34 to a signal with a given higher frequency;38 a local oscillator adapted to supply a signal with a given frequencyf1 (for example, 14 MHz) to the first frequency conversion circuit 36 aswell as a second frequency conversion circuit 44 to be described later;40 a 0.5 H glass delay line (for example, with an operation frequency of14˜26 MHz) which is used to delay the field signal output from the firstfrequency conversion circuit 36 only by 0.5 H; 42 a high-pass filterwhich permits to pass through the upper side band portion (with afrequency of 14˜26 MHz) of the side band of the field signal that isoutput through the 0.5 H delay line 40; 44 a second frequency conversioncircuit adapted to convert the field signal output through the high-passfilter 42 into a field signal with a given lower frequency; and, 46 alow-pass filter adapted to permit to pass through the field signal (witha frequency of 0.15-12 MHz) output from the second frequency conversioncircuit 44. In addition, 48 designates a signal switch circuit adaptedto select a field signal that is supplied direct from the amplifier 34and a field signal that is delayed 0.5 H; 50 an FM brightness signaldemodulation circuit adapted to demodulate an FM brightness signal Y ofa frame signal output through the signal switch circuit 48; 52 a signalprocess circuit which comprises a de-emphasis circuit to correct thecharacteristic of the brightness signal Y demodulated by the FMbrightness signal demodulation circuit 50 such that the pre-emphasischaracteristic of the brightness signal Y that is given thereto when itis recorded is corrected into an inverted characteristic, and othercircuits; and, 56 a signal process circuit which comprises a de-emphasiscircuit to correct the characteristic of the chroma signal C demodulatedby an FM chroma signal demodulation circuit 54 such that thepre-emphasis characteristic of the chroma signal C given thereto when itis recorded is converted to an inverted characteristic, and othercircuits.

Next, description will be given of the operation of the above-structuredembodiment in connection with FIG. 5.

The field signal that is recorded on the track of the magnetic disc 30is reproduced repeatedly by the magnetic head 32 (FIG. 5(a)) and is thenamplified by the amplifier 34, before the field signal is supplied tothe contact a of a switch SW3 of the signal switch circuit 48. Also, thefield signal output from the amplifier 34 is supplied to the firstfrequency conversion circuit 36, where the field signal is mixed with asignal with a frequency f1 output by the local oscillator 38 to providea difference signal component (lower side bands f1-fc, f1-fy) and a sumsignal component (upper side bands f1+fc, f1+fy) (FIG. 5(b)), which arethen supplied through the 0.5 H glass delay line 40 to the high-passfilter 42. Such field signal is structured such that the upper sidebands are set in a frequency band in the neighborhood of a primary sideband of the FM brightness signal Y and higher than 10 MHz. The high-passfilter 40 allows only the sum signal component in a frequency bandhigher than the frequency f1 (for example, a signal component with afrequency of 14 MHz or higher) of the sum and difference signalcomponents of the field signal to transmit therethrough, and the sumsignal component is then supplied to the second frequency conversioncircuit 44. In the second frequency conversion circuit 44, the sumsignal component is mixed with the signal with the frequency f1 comingfrom the local oscillator 38 to be converted again to a field signalhaving a low frequency (fc+fy). Then, the low frequency field signal ispassed through the low-pass filter 46 and is then supplied to thecontact b of the switch SW3 of the signal switch circuit 48. The fieldsignal that is supplied from the amplifier 34 direct to the signalswitch circuit 48 and the field signal that is supplied after it isdelayed by 0.5 H are selected alternately at each of 1 V by the switchSW3 to be supplied to the demodulation circuits 50, 54 as the framesignal. The FM brightness signal Y of the frame signal is demodulated bythe FM brightness signal demodulation circuit 50 and the thusdemodulated brightness signal is given corrections such as a de-emphasiscorrection and the like by the signal process circuit 52. Also, the FMchroma signal C of the frame signal is demodulated by the FM chromasignal demodulation circuit 54 and the thus demodulated chroma signal isgiven corrections such as a de-emphasis correction and the like by thesignal process circuit 56. And, based on the birghtness signal Y outputfrom the signal process circuit 52 as well as on the chroma signal fromthe signal process circuit 56, a video signal of a given frame can becomposed.

As described above, in the above embodiment, the field signal in whichthe brightness signal component and chroma signal component thereof arefrequency modulated and frequency multiplexed is once converted to asignal having a higher frequency band, the converted field signal isdelayed only by 0.5 H by the 0.5 H glass delay line which has a wideband frequency characteristic, and the delayed field signal is convertedagain to a field signal with its original frequency, before the framesignal is created. Therefore, according to the present embodiment, acircuit configuration can be simplified and, since there is producedalmost no difference in delay time between the brightness and chromasignals, there is eliminated the possibility that color discrepanciesmay be produced in the image reproduced.

Also, according to the present embodiment, since the delay of thebrightness and chroma signals is performed prior to demodulationthereof, there is eliminated the possibility of flickers being produced.

Referring next to FIG. 6, there is illustrated a further embodiment of areproducing system employed in a magnetic recording/reproducingapparatus to which the invention is applied.

In FIG. 6, a reference character 60 designates a magnetic disc which isone of magnetic recording mediums; 62 a magnetic head adapted toreproduce a field signal which is composed of a frequency modulated (FM)brightness signal Y (for example, a signal with a frequency bandwidth offy=2.5˜12 MHz) and an FM chroma signal C (for example, a signal with afrequency bandwidth of fc=0.15˜2.5 MHz) respectively recorded on thetrack of the magnetic disc 60; 64 an amplifier adapted to amplify thefield signal that is reproduced by the magntic head 62; 66 an FMbrightness signal demodulation circuit adapted to demodulate the FMbrightness signal Y of the field signal output from the amplifier 64;and, 68 an FM chroma signal demodulation circuit adapted to demodulatethe chroma signal C. Also, numeral 70 designates a frequency conversioncircuit adapted to convert the field signal output from the amplifier 64into a field signal which has a frequency higher than that of the FMbrightness signal Y; 72 a local oscillator adapted to supply a signalwith a given frequency f1 (for example, 14 MHz) to the frequencyconversion circuit 70; 74 a 0.5 H glass delay line (for example, a linehaving an operation frequency of 14˜26 MHz) adapted to delay the fieldsignal output from the frequency conversion circuit 70 only by 0.5 H; 76a high-pass filter which allows only the upper side band portion (in thefrequency range of 14˜26 MHz) of the side band of the field signal thatis output through the 0.5 H glass delay line to pass therethrough; 78 anFM brightness signal demodulation circuit adapted to demodulate the FMbrightness signal Y of the field signal that has passed through thehigh-pass filter 76; and, 80 an FM chroma signal demodulation circuitadapted to demodulate the FM chroma signal C of the field signal. Inaddition, 82 designates a signal switch circuit which comprises a switchSW1 to select the demodulated brightness signals Y respectively outputfrom the FM brightness signal demodulation circuit 66 and FM brightnesssignal demodulation circuit 78, and a switch SW2 to select thedemodulated chroma signal C respectively output from the FM chromasignal demodulation circuit 68 and FM chroma signal demodulation circuit80; 84 a signal process circuit which comprises a de-emphasis circuitadapted to correct the characteristic of the brightness signal Y that isoutput via the switch SW1 of the signal switch circuit from thepre-emphasis characteristic that is given when the signal is recorded tothe reversed characteristic thereof, and other circuit; and, 86 a signalprocess circuit which comprises a de-emphasis circuit adapted to correctthe characteristic of the chroma signal C output via the switch SW2 fromthe pre-emphasis characteristic given in recording to the reversedcharacteristic thereof, and other circuits.

Next, description will be given below of the operation of theabove-structured embodiment in connection with FIG. 7.

The field signal that is recorded on the track of the magnetic disc 60is repetitively reproduced by the magnetic head 62 (FIG. 7(a)), and thefield signal is then amplified by the amplifier 64 before it is suppliedto the FM brightness signal demodulation circuit 66 and FM chroma signaldemodulation circuit 68. Then, the brightness signal Y that isdemodulated by the demodulation circuit 66 is supplied to the contact aof the switch SW1 and the chroma signal C demodulated by thedemodulation circuit 68 is supplied to the contact a of the switch SW2,respectively. Also, the field signal output from the amplifier 64 issupplied to the frequency conversion circuit 70 where it is then mixedwith the signal with the frequency of f1 output from the localoscillator 72, with the result that the mixed signal is output from theconversion circuit 70 in the form of a difference signal componentthereof (in the lower side bands, f1-fc, f1-fy) and in the form of a sumsignal component thereof (in the upper side bands, f1+fc, f1+fy) (FIG.7(b)) and is then supplied through the 0.5 delay line 74 to thehigh-pass filter 76. The high-pass filter 76 transmits only the sumsignal component in the band (for example, a signal component with afrequency of 14 MHz or higher) higher than the frequency f1 out of theabove-mentioned sum and difference signal components of the field signaland the sum signal component is then supplied to the demodulationcircuit 78, 80 (FIG. 7(c )). Then, the brightness signal Y that isdemodulated by the demodulation circuit 78 is supplied to the contact bof the switch SW1 of the signal switch circuit 82, and the chroma signalC demodulated by the demodulation circuit 80 is then supplied to thecontact b of the switch SW2 of the signal switch circuit 82. Therespective brightness signals respectively supplied to the contacts aand b of the switch SW1 of the signal switch circuit 82 are selectedalternately at every one vertical scan period (V) and thus each of thebrightness signals is then supplied to the signal process circuit 84 asthe brightness signal Y of the frame. Also, the respective chromasignals C respectively supplied to the contacts a and b of the switchSW2 of the signal switch circuit 82 is selected alternately at every 1V, similarly as in the brightness signals Y, and each of them is thensupplied to the signal process circuit 86 as the frame chroma signal C.And, based on the brightness signal Y that is processed by the signalprocess circuit 84 such as the de-emphasis correction or the like aswell as on the chroma signal C processed by the signal process circuit86 such as the de-emphasis correction or the like, a video signal of agiven frame can be composed.

As described above, in the present embodiment, the frequency modulatedfield signal composed of brightness and chroma signal components whosefrequencies are multiplexed is once converted into a field signal in ahigh frequency band in which a relatively better demodulationcharacteristic can be obtained by a demodulator, and the high frequencyband field signal is then delayed only 0.5 H by a 0.5 H glass delay linewhich has a wide band frequency characteristic, before a frame signal iscreated. Therefore, according to the present embodiment, a circuitconfiguration can be simplified and also since there is almost nodifference in delay time between the brightness and chroma signals,there is eliminated the possibility that color discrepancies may beproduced in a reproduced image.

Also, according to the present embodiment, due to the fact that thebrightness and chroma signals are both delayed before they aredemodulated, there is eliminated the possibility that flickers may beproduced.

Referring next to FIG. 8, there is shown a still further embodiment of areproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied.

This embodiment, as in the before-mentioned embodiments, aims atpreventing the occurrences of color discrepancies and flickers found inthe prior art systems due to the fact that two kinds of delay lines areused to delay the brightness and chroma signals 0.5 H separately.Especially, this embodiment is applied to prevent a vertical jitter(which is referred to as V jitter hereinafter) which may occur when afield signal is converted into a frame signal. Prior to description ofthe embodiment in FIG. 8, the V jitter will be explained.

There is employed a so-called field/frame conversion system in which aframe signal is formed of one kind of field signals by using the strongvertical correlation of a video signal as well as by scanning the samerecorded portion twice. In this field/frame conversion system, sincefield signals can not be divided into odd fields and even fields simplyby repeating the same field signal, as shown in FIG. 9, the same fieldsignal that has been reproduced repetitively is passed through a 0.5 Hdelay line 2 so as to provide a non-delay field signal and a 0.5 Hdelayed field signal by means of a change-over switch 3, and the twotypes of field signals are selected alternately at every one verticalscan period (1 V) to thereby obtain an odd field and an even field, thatis, a field signal 1 is converted to a frame signal 5. However, sincethe time interval between two successive vertical synchronizationsignals, as they are, is delayed 0.5 H from 1 V, it is considered thatthe contacts 3a, 3b of the change-over switch 3 are selected in such amanner as shown in FIG. 10. That is, by use of a switch control signal6, the 0.5 H delay field signal 4 is selected in a portion 7 rangingfrom a front equalization pulse section to a back equalization pulsesection out of a period to select the non-delay field signal 1. At anyrate, in order to convert the field signal to the frame signal, as shownin FIG. 9, there is used a circuit which is adapted to select thenon-delay signal and the 0.5 H delay signal.

In this manner, one kind of field signals can be used to form aninterlaced-scan frame signal and an image based on such frame signal canbe reproduced on a television screen. However, in this case, there isproduced a V jitter in the image. The V jitter means thevertical-direction (V direction) displacements of the image that arerepeated at a field cycle on the television screen image, eachdisplacement having a width of one horizontal scan line (1 H). That is,in this case, the television screen image is vibrated vertically with 1H width at a field cycle (1/60 sec.).

As effective means to prevent the occurrence of such V jitter,conventionally, there has been employed a technique to use an arithmeticmean of odd-field brightness signals. That is, a 1 H delay brightnesssignal is added to a non-delay brightness signal and the sum of them isthen divided by 2 to obtain a signal; and, the thus obtained signal isused as an odd-field brightness signal.

Now, referring back to FIG. 8, a magnetic head 110 is connected to theinput terminal of the amplifier 111 and the output terminal of theamplifier 111 is connected to the input terminal of a first frequencyconverter 112, whereby the frequency modulated field signal that isrepetitively reproduced by the magnetic head 110 is first amplified bythe amplifier 111 and then can be supplied to the first frequencyconverter 112.

A signal with a given frequency f1 (for example, a frequency of theorder of 28 MHz) to be oscillated in a local oscillator 113 is suppliedto the first frequency converter 112, where the signal with thefrequency f1 and the above-mentioned field signal are mixed together tothereby provide a sum signal and a difference signal thereof.

The above-mentioned field signal is composed of a brightness signal witha frequency bandwidth of fy and a chroma signal with a frequency bandwidth of fc and it has a bandwidth of fc+fy (for example, 0˜10 MHz). Thefirst frequency converter 112 is configured as a circuit which isadapted to be able to obtain a signal having a higher-band frequency asthe output thereof, that is, it can provide a signal with a frequency offc+fy+f1 (for example, 28˜38 MHz) at the output thereof.

The output terminals of the first frequency converter 112 are connectedto the input terminals of a 0.5 H delay line 115 and a second frequencyconverter 118 as well as to the contact b of a field/frame conversionswitch 124 which is used to perform the field/frame conversion of thechroma signals.

Also, the output terminal of the 0.5 H delay line 115 is connectedthrough another 0.5 H delay line 116 to a second frequency converter 117as well as to the input terminal of another second frequency converter119 and the contact a of the field/frame conversion switch 124.

A signal with a frequency f1 (28 MHz or so) can be supplied from thelocal oscillator 113 to the respective second frequency converters 117,118, and 119.

Here, the 0.5 H delay lines 115 and 116 are respectively glass delaylines each having a wide band frequency characteristic and the frequencycharacteristic and group delay characteristic thereof are as shown inFIG. 3. As described before, each of the glass delay line has abandwidth of 16˜44 MHz. Since the frequency bandwith of the outputsignal of the first frequency converter 112 is 28˜38 MHz, when theabove-mentioned glass delay line is used, then there can be provided asufficient bandwidth, so that there arises no problem with respect tothe frequency characteristic of the glass delay line.

Also, with respect to the group delay characteristic of theabove-mentioned glass delay line, the range of variations of the delaytime in the bandwidth of 16˜44 MHz is within 100 n sec. This range ofdelay time variations produces such slight color discrepancies that canbe neglected in practial uses.

Now the 0.5 H delay line 115 is used to delay only 0.5 H the frequencymodulated field signal in the field/frame conversion operation and theother 0.5 H delay line 116 is used 115 to delay the frequency modulatedfield signal (the output signal of the first frequency converter 112) 1H with the above-mentioned 0.5 H delay line so as to obtain a fieldsignal which is necessary to perform the arithmetic mean operation ofthe brightness signals.

The second frequency converters 117, 118 and 119 are respectivelyadapted to receive the output signals (with a frequency of fc+fy+f1, forexample, 28˜38 MHz) of the first frequency converter 112 through the 0.5H delay lines 115 and 116, or directly from the first frequencyconverter 112, or through only the 0.5 H delay line 115, and to mixthese signals with the output signals of the first local oscillator 113so as to provide the difference signals (with a frequency of fc+fy)thereof. The output terminals of the second frequency converters 117 and118 are respectively connected to high-pass filters 122 and brightnesssignal process circuit 123 and further to a addition circuit 120 whichis adapted to calculate the arithmetic mean of these output signals.

Also, the output terminal of the addition circuit 120 is connected to acontact a of a field/frame conversion switch 121 and the other contact bof the switch 121 is connected through another brightness signal processcircuit 123 and high-pass filter 122 to the output terminal of thesecond frequency converter 119. The field/frame conversion switch 121 iscomposed of an analog switch which is adapted to select alternately afield signal 100 output from the addition circuit 120 and a field signaloutput from the second frequency converter 119 at every one verticalscan period (1 V) according to a control signal 102 to thereby convertthem into a frame signal 104.

To the output terminals of the second frequency converters 117 to 119there are connected the high-pass filters (with a frequency of fy, forexample, 2.5˜10 MHz) and the brightness signal process circuits 123, sothat a brightness signal Y can be reproduced through these high-passfilters 122 and brightness signal process circuit 123. Here, each of thebrightness signal process circuit 123 is composed of a frequencymodulated signal demodulator, a de-emphasis circuit and the like and isused to create the brightness signal Y.

On the other hand, the field/frame conversion switch 124 is a switchwhich is used to carry out the field/frame conversion operation on thechroma signals. The contact a of the switch 124 is connected via thesecond frequency converter 126 to the output terminal of the 0.5 H delayline 115, and the contact b thereof is connected to the output terminalof the amplifier 111. The field/frame conversion switch 124 selects afield signal 132 that is delayed 0.5 H and output through the secondfrequency converter 126 from the 0.5 H delay line 115 and a non-delayfield signal 107 alternately at every one vertical scan period accordingto a control signal 106 so as to obtain a frame signal 108.

The above-mentioned second frequency converter 126 is a circuit which isadapted to receive a signal with a frequency of f1 oscillated from thelocal oscillator 113 and mix it with the above-mentioned chroma signalcomponent (with a frequency fc+f1) to thereby obtain the differencetherebetween, that is, provide the original chroma signal component witha frequency fc. The original chroma signal component fc is then input toa chroma signal process circuit 128 where line sequentialized colordifference signals R-Y, B-Y are created. The color difference signalsR-Y, B-Y are then output to an NTSC encoder 129 which is adapted to mixthe color difference signals R-Y, B-Y with the brightness signals Youtput from the brightness signal process circuits 123 to thereby createa given format of NTSC composite signal.

Now, we will describe the operation of the circuits in the reproducingsystem of the magnetic recording/reproducing apparatus constructed inthe above-mentioned manner.

The field signal with a frequency bandwidth of fc+fy that is repeatedlyreproduced by the magnetic head 110 is first amplified by the amplifier111 and is then supplied to the first frequency converter 112. The fieldsignal supplied to the first frequency converter 112 is mixed with thesignal with a frequency of f1 output from the local oscillator 113 toprovide the sum signal component of a higher frequency band (with afrequency of fc+fy+f1) which is in turn output from the first frequencyconverter 112. The output signals of the first frequency converter 112are supplied to the 0.5 H delay line 115 and the second frequencyconverter 118, respectively. A a result of this, the field signal thatis delayed 1 H by 0.5 H delay lines 115, 116 is input to the frequencyconverter 117, the non-delay field signal is input to the secondfrequency conver 118, and the field signal that is delayed only 0.5 H isinput to the second frequency converter 119. These field signals arethen converted by the second frequency converters 117, 118, and 119 intothe field signal with a frequency bandwidth of fc+fy. And, the fieldsignals that are output from the second frequency converters 117 and 118are respectively input via the high-pass filters 122 and brightnesssignal process circuit 123 to the addition circuit 120, and in theaddition circuit 120 these signals are processed to obtain a signal 100representing the arithmetic mean thereof, which signal is then suppliedto the contact a of the field/frame conversion switch 121.

On the other hand, to the other contact b of the field/frame conversionswitch 121 is input a field signal 101 that is delayed only 0.5 Hthrough the second frequency converter 119, high-pass filter 122 andbrightness signal process circuit 123. These field signals 100, 101 areselected alternately at every one vertical scan period according to thecontrol signal 102 to be converted into a frame signal 104. In thebrightness signal process circuit 123, the brightness signal componetinput thereto is demodulated and is then de-emphasized so as to createthe brightness signal Y. The thus created brightness signal Y is theninput to the NTSC encoder 129.

Also, a non-delay field signal 107 output from the amplifier 111 and afield signal 132 that is delayed only 0.5 H and is obtained via thefirst frequency converter 112, 0.5 H delay line 115 and second frequencyconverter 126 are selected alternately at every one vertical scan periodby the field/frame conversion switch 124 according to a control signal106 to be converted into a frame signal 108, so that the two linesequentialized color difference signals R-Y, B-Y can be created. The twocolor difference signals are output to the NTSC encoder 129 and in theNTSC encoder 129 these two color difference signals R-Y, B-Y are mixedwith the brightness signals Y output from the brightness signal processcircuits 123 to thereby create the NTSC composite signal, which is thenoutut therefrom.

As described above, in the present embodiment, the frequency modulatedfield signal is once converted into the field signal with a higher bandof frequencies and the higher frequency field signal is then delayedonly 0.5 H by use of the 0.5 H glass delay line which has a wide bandfrequency characteristic and also has a good group delay characteristic,before the frame signal is created. Therefore, according to the presentembodiment, there is produced almost no difference in delay time betweenthe brightness and chroma signals, which eliminates the possibility ofthe color discrepancies being generated in the reproduced image.

Also, the 0.5 H glass delay line used in the present embodiment has awider signal band over the conventional CCD (charge coupled device),which can reduce the signal degradation, that is, a better S/N(signal-to-noise ratio) can be obtained. For this reason, according thepresent embodiment, it is possible to obtain a frame signal which isexcellent in S/N.

Further, according to the present embodiment, since the field signal,with the brightness signal component and chroma signal component thereofremaining mixed together, can be converted into the frame signal, acircuit configuration can be simplified.

Moreover, in the prsent embodiment, due to the fact that the fieldsignal can be converted, in the frequency modulated state, into theframe signal, there is eliminated the possibility that flickers may beproduced by the switching operation of the field/frame conversionswitch.

In addition, according to the present embodiment, since the arithmeticmean is employed in the field/frame conversion of the brightnesssignals, it is possible to prevent the occurrence of the V jitter and ashade of the reproduce image can occur continuously.

Referring now to FIG. 11, there is shown a further embodiment of areproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied. In FIG. 11, a magnetic head 210 isconnected to the input terminal of an amplifier 211 and the outputterminal of the amplifier 211 is connected to the input terminal of afirst frequency converter 212, whereby a field signal that isrepetitively reproduced by the magnetic head 210 is first amplified bythe amplifier 211 and is then supplied to the first frequency converter212. To the first frequency converter 212 there an be supplied a signalwith a given frequency of f1 (for example, 28 MHz or so) which isoscillated in a first local oscillator 213 and, in the first frequencyconverter 212, the signal with a frequency of f1 is mixed with theabove-mentioned field signal so as to be able to obtain a sum signal anda difference signal thereof. The above-mentioned field signal iscomposed of a brightness signal with a frequency bandwidth of fy and achroma signal with a frequency bandwidth of fc, and thus the fieldsignal has a bandwidth of fc+fy (for example, 0˜10 MHz). The firstfrequency converter 212 is a circuit which is adapted to be able toobtain as the output terminal thereof a signal having a frequency in thehigher frequency band, that is, at the output thereof there can beobtained a signal which has a frequency of fc+fy+f1 (for example, 28˜38MHz). The output terminal of the first frequency converter 212 isconnected to one contact a of a field/frame conversion switch 214 and itis also connected to the other contact b of the field/frame conversionswitch 214 through a 0.5 H delay line 215 which may be composed of aglass delay line or the like having a wide band frequencycharacteristic, whereby the output signal (with a frequency of fc+fy+f1)of the first frequency converter 212 can be applied intact to the onecontact a of the field/frame conversion switch 214 as well as it canalso be applied through the 0.5 H delay line 215 to the other contact bof the switch 214. The field/frame conversion switch 214 is composed ofan analog switch which is adapted to select a non-delay field signal 216and a field signal 217 through the 0.5 H delay line 215 alternately atevery one vertical scan period (1 V) according to a control signal 218to thereby convert into a frame signal 219. The output terminal of thefield/frame conversion switch 214 is connected to a second frequencyconverter 220 and a band-pass filter 221, so that the frame signal 219output from the switch 214 can be supplied to the second frequencyconverter 220 and band-pass filter 221.

The second frequency converter 220 is a circuit which is adapted toreceive the signal with an oscillation frequency of f1 output from thefirst local oscillator 213 and to mix it with the frame signal (with afrequency of fc+fy+f1) so as to provide a difference signal (with afrequency of fc+fy) thereof. The output terminal of the second frequencyconverter 220 is connected through a high-pass filter 222 to abrightness signal demodulation circuit 223, so that the output signal(with a frequency of fc+fy, for example 0˜10 MHz) from the secondfrequency converter 220, after it passes through the high-pass filter222 and thus it becomes a brightness signal component (with a frequencyof fy, for example, 2.5˜10 MHz), can be demodulated by the brightnesssignal demodulation circuit 223 into a brightness signal Y.

The band-pass filter 221 is a filter with a given bandwidth (forexample, 28±2.5 MHz) which is adapted to be able to take the chromasignal component (with a frequency of fc+f1, for example, 28˜30.5 MHz)out of the frame signal 219 and supply it to a third frequency converter224. The third frequency converter 224 is a circuit which is adapted tobe able to receive a signal with a local frequency of f2 (for example,24 MHz) that is oscillatd by a second local oscillator 225 and mix itwith the above-mentioned chroma signal component (with a frequency offc+f1) to thereby provide a difference component (with a frequency offc+f1-f2, for example, 4˜6.5 MHz) thereof. The output signal (chromasignal component) from the third frequency converter 224 is applied to achroma signal demodulation circuit 226 in which a chroma signal can beobtained.

We will describe the operation of the above-constructed embodiment.

The field signal with a frequency bandwidth of fc+fy that isrepetitively reproduced by the magnetic head 210 is first amplified bythe amplifier 211 and is then supplied to the first frequency converter212. The field signal supplied to the first frequency converter 212 ismixed with the signal with a frequency of f1 output from the first localoscillator 213 to provide a sum signal component (with a frequency offc+fy+f1) which is then output from the first frequency converter 212.The signal output from the first frequency converter 212 is divided intotwo signals: that is, one is a signal 216 which is supplied intact tothe one contact a of the field/frame conversion switch 214; and, theother is a signal 217 which is passed through the 0.5 H delay line 215and is then supplied to the other contact b of the switch 214. These twokinds of signals are selected alternately at every 1 V by the switch 214to be converted into the frame signal 219 and the thus created framesignal 219 is then supplied to the second frequency converter 220 andband-pass filter 221.

The frame signal 219 that is supplied to the second frequency converter220 is mixed here with the signal output from the first local oscillator213 to be converted again to the signal with a low frequency of fc+fy.When the signal with this frequency of fc+fy is passed through thehigh-pass filter 222, then there can be obtained only the brightnesssignal component (fy). And, the brightness signal component (fy) isapplied to the brightness signal demodulation circuit 223 to therebyprovide the brightness signal Y.

On the other hand, the frame signal that has passed through theband-pass filter 221 provides the chroma signal component with a givenbandwidth of fc+f1, which is in turn supplied to the third frequencyconverter 224. The chroma signal component thus supplied to the thirdfrequency converter 224 is mixed with the signal output from the secondlocal socillator 225. In the third frequency converter 224, thedifference component thereof is taken out. The difference component isselected so as to have a frequency that is ideal for the chroma signaldemodulation circuit 226 to demodulate the difference component.

As mentioned above, according to the present embodiment, since the fieldsignal, while the brightness signal component and chroma signalcomponent thereof are maintained in the frequency multiplexed condition,can be converted to the frame signal, a simplified circuit configurationis possible. Also, due to the fact that the chroma signal component canbe demodulated at a frequency which is suitable for chroma demodulation,the chroma reproduction can be improved.

Further, according to the present embodiment, since the brightness andchroma signals are respectively delayed 0.5 H in the frequency modulatedconditions thereof before they are demodulated, it is possible toprevent the occurrence of flickers.

Referring next to FIG. 12, there is shown another embodiment of areproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied. In this embodiment as well, the sameparts as in the last-mentioned embodiment are given the samedesignations for convenience of description thereof.

The embodiment shown in FIG. 12 is different from the last-mentionedembodiment in connection with FIG. 11 in that the field/frame conversionis performed in a lower frequency (for example, 0˜10 MHz), but thepresent embodiment is similar to the last-mentioned embodiment in thesubject matter thereof, that is, they are similar to each other in thatthe 0.5 H delay is carried out at a higher frequency and that the chromasignal demodulatin is performed at an optimum frequency. In other words,according to the prsent embodiment, there is provided a circuitconfiguration in which a field signal with a frequency of fc+fy that isrepetitively reproduced by the magnetic head 210 is first amplified bythe amplifier 211 and is then divided into two signals: one of them is asignal 216A which is supplied intact to the one contact a of thefield/frame conversion switch 214; and, the other is a signal 217A whichis once converted to a field signal with a high frequency of fc+fy+f1(for, example, 28˜38 MHz), is next delayed 0.5 H by the 0.5 H delay line215 and is then converted back again to the field signal with theoriginal frequency (fc+fy, for example, 0˜10 MHz) by the secondfrequency converter 220 before it is supplied to the other contact b ofthe conversion switch 214. The conversion switch 214 is a switch whichis adapted to select the above-mentioned respective signals 216A and217A alternately at every 1 V in accordance with the control signal 218to obtain a frame signal 219A. The frame signal 219A output from theswitch 214 is to be input to the high-pass filter 222 and low-passfilter 230.

The output of the high-pass filter 222 is to be supplied to thebrightness signal demodulation circuit 223.

The low-pass filter 230 is a circuit which is adapted to transmittherethrough only the chroma signal component with a frequency of fc(for example, 0˜2.5 MHz) out of the frame signal 219A. The outputterminal of the low-pass filter 230 is connected to a frequencyconverter 231, so that the above-mentioned chroma signal component canbe supplied to the frequency converter 231. A signal with a givenfrequency of f3 (for example, 4 MHz) that is oscillated by a localoscillator 232 can be supplied to the frequency converter 231. In thefrequency converter 231, the chroma signal component and the signal fromthe local oscillator 232 are mixed together to thereby provide a sumsignal component and a a difference signal component therof. The outputterminal of the frequency converter 231 is connected through a band-passfilter 233 to the chroma signal demodulation circuit 226, so that theoutput signal from the frequency converter 231 can be filtered by theband-pass filter 233 with a given bandwidth of fc+f3 (4˜6.5 MHz) beforeit can be supplied to the chroma signal demodulation circuit 226.

Now, the operation of the thus structured embodiment will be describedbelow.

The field signal that is repetitively reproduced by the magnetic head210 is first amplified by the amplifier 211 and is then applied to theone contact a of the above-mentioned switch 214 and at the same timesupplied to the first frequency converter 212. The field signal that isgiven to the first frequency converter 212 is once converted to a fieldsignal with a high frequency of fc+fy+f2 and is then supplied to the 0.5H delay line 215. The high frequency field signal is delayed 0.5 H bythe 0.5 H delay line 215 and the 0.5 H delayed field signal is againconverted to the signal with a low frequency of fc+fy by the secondfrequency converter 220, before it is applied to the other contact b ofthe switch 214. The signal 216A applied to the one contact a of theswitch 214 and the signal 217A applied to the other contact b of theswitch 214 are selected alternately at every 1 V to the converted to theframe signal 219A.

The frame signal 219A is given through the high-pass filter 222 to thebrightness signal demodulation circuit 223 to provide the brightnesssignal Y.

Also, when the frame signal 219A is passed through the low-pass filter230, then only the chroma signal component (fc) thereof is extracted.The chroma signal component (fc) is mixed with the signal with afrequency (f3) output from the local oscillator 232 in the frequencyconverter 231 and the sum component (fc+f3) thereof is taken out throughthe band-pass filter 233 and is then applied to the chroma signaldemodulation circuit 226 so as to obtain the chroma signal C.

According to the present embodiment, in addition to the effects of theabove-mentioned embodiment, since the switching operation to perform thefield/frame conversion can be carried out in the low frequency, there isobtained an effect that it is easy to configure a circuit.

Referring now to FIG. 13, there is shown a block diagram of anembodiment of the above-mentioned demodulation circuits 223, 226.

The brightness signal component (fy) that has been converted to theframe signal is passed through a limiter 241, is demodulated by afrequency modulated signal demodulator 242, and is passed through ade-emphasis circuit 243 having a characteristic corresponding to apre-emphasis characteristic given when a signal is recorded, with theresult that the brightness signal component can provide a brightnesssignal Y of a base band. Also, the line sequential chroma signal(fc+f1-f2) converted to the frame signal is passed through a limiter244, is demodulated by a frequency modulated signal demodulator 245, andis then passed through a de-emphasis circuit 246 having a characteristiccorresponding to the pre-emphasis characteristic given during recordingso as to provide a line sequential color difference signal C of a baseband. The line sequential color difference signal C is separated by a 1H delay line 248 and a synchronizing switch 248 into two colordifference signals R-Y, B-Y. The synchronizing switch 248 is adaptedsuch that the selection of the contacts c and f thereof an the selectionof the contacts d and e can be executed at every 1 H according to acontrol signal 249. As a result of this, the portions of the respectivecolor difference signals that have been omitted at every 1 H inrecording can be supplemented by the signals of 1 H before, so that thecontinuous R-Y, B-Y color difference signals can be obtained.

The brightness signal Y and two color difference signals R-Y, B-Y of abase band obtained in the above-mentioned manner are converted by anencoder 250 to NTSC signal 251, as occasion demands, which are given toa television receiver, a monitor television receiver and the like.

Referring next to FIG. 14, there is shown a further embodiment of areproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied.

In FIG. 14, a magnetic head 310 is connected to the input terminal of anamplifier 311 and the output terminal of the amplifier 311 is connectedto the input terminal of a first frequency converter 312, whereby thefield signal that is reproduced by the magnetic head 310 can beamplified by the amplifier 311 and also can be then supplied to thefirst frequency converter 312. To the first frequency converter 312 issupplied a signal with a given frequency of f1 (for example, 28 MHz)that is oscillated in a first local oscillator 313. The first frequencyconverter 312 is a circuit which is adapted to mix a signal with afrequency of fc+fy (for example, 0˜10 MHz), which is composed of abrightness signal with a frequency of fy (for example, 2.5˜10 MHz) and achroma signal with a frequency of fc (for example, 0.5˜2.5 MHz), withthe signal with a frequency of f1 from the local oscillator 313 so as toobtain a sum signal thereof with a frequency of fc+fy+f1 (for example,28˜38 MHz). The output terminal of the first frequency converter 312 isconnected through a 0.5 H delay line 314 (for example, a glass delayline) having a wide band frequency characteristic to a second frequencyconverter 315 and a band-pass filter 316 having a pass band of fc+f1,whereby the signal with a frequency of fc+fy+f1 from the first frequencyconverter 312 can be delayed 0.5 H by the delay line 314 and then can besupplied to the second frequency converter 315 and band-pass filter 316.As can be seen from the foregoing description, since the delay line 314is used at the high frequency, there can be obtained a sufficientfrequency bandwidth. Now, the output terminal of the second frequencyconverter 315 is connected to one contact b of a field/frame conversionswitch 317. The second frequency converter 315 is a circuit which isadapted to mix the local oscillation signal with a frequency of f1 fromthe first local oscillator 313 with the signal with a frequency offc+fy+f1 from the 0.5 H delay line 314 and also to supply a differencesignal thereof with a frequency of fc+fy+f1-f1 to the one contact b ofthe switch 317.

The other contact a of the switch 317 is connected to the outputterminal of the amplifier 311, whereby a non-delay field signal with afrequency of fc+fy from the amplifier 311 can be supplied to contact a.The switch 317 is composed of an analog switch which is adapted toselect the non-delay field signal 319 and the 0.5 H delayed field signal320 alternately at every one vertical scan period (1 V) in accordancewith a control signal 318 to convert into a frame signal 321 and also tosupply the frame signal 321 to a high-pass filter 322. This high-passfilter 322 is a circuit which transmits therethrough only the brightnesssignal with a frequency of fy out of the frame signal with a frequencyof fc+fy and also supplies the brightness signal to a brightness signaldemodulation circuit 323. The brightness signal demodulation circuit 323is a circuit adapted to demodulate the above-mentioned brightnesssignal.

On the other hand, the band-pass filter 316 is a circuit which isadapted to select the signal with a frequency of fc+f1 (for example,28˜30.5 MHz) out of the 0.5 H delayed field signal with a frequency offc+fy+f1 and also to supply it to a third frequency converter 324. Asecond local oscillator 325 is connected to the third frequencyconverter 324, so that an oscillation signal with a frequency of f2 (forexample, 24 MHz) that is oscillated in the second local oscillator 325can be supplied to the third frequency converter 324. The thirdfrequency converter 324 a circuit which is adapted to mix a signal witha frequency of fc+f1 from the band-pass filter 316 with the oscillationsignal with a frequency of f2, to thereby provide a difference signal326 thereof with a frequency of fc+f1-f2 (for example, 4˜6.5 MHz) andalso to supply the difference signal 326 to one contact b of afield/frame conversion switch 327. This switch 327 is composed of ananalog switch which is adapted to select the signals at the two contactsa, b alternately at every one vertical scan period (1 V) according to acontrol signal 328 to convert them into the frame signal.

The output terminal of the amplifier 311 is connected through a low-passfilter 329 to the input terminal of a fourth frequency converter 330, sothat the low-pass filter 329 can extract only the component fc out ofthe field signal with frequency of fc+fy and also can supply it to thefourth frequency converter 330. To the fourth frequency converter 330 isconnected a third local oscillator 331, so that an oscillation signalwith a local oscillation frequency of f3 (for example, 4 MHz) can beapplied to the fourth frequency converter 330. This fourth frequencyconverter 330 is a circuit which is adapted to mix the non-delay fieldsignal with a frequency of fc input thereto with the oscillation signalwith a frequency of f3 output from the third local oscillator 331 tothereby obtain a sum signal thereof having a frequency of fc+f3 (forexample, 4˜6.5 MHz) 332 and also to supply the sum signal to the othercontact b of the switch 327.

The above-mentioned switch 327 is a switch which is adapted to select a0.5 H delayed signal 326 and a non-delay signal 332 alternately at every1 H to convert them into a frame signal 333 with a frequency offc+f1-f2=fc+f3 (for example, 4˜6.5 MHz) and also to supply the framesignal 333 to a band-pass filter 334. The band-pass filter 334 is acircuit which transmits the frame signal therethrough and also suppliesit to a chroma signal demodulation circuit 335 adapted to demodulate theframe signal into a chroma signal.

Next, the operation of the present embodiment will be described below.

The signal with a frequency of fc+fy (0˜10 MHz) that is repetitivelyreproduced by the magnetic head 310 is first amplified by the amplifier311 and, after then, is supplied to the first frequency converter 312and low-pass filter 329 as well as supplied to the contact a of theswitch 317 as the non-delay field signal 319. The signal with afrequency of fc+fy that is supplied to the first frequency converter 312is mixed here with the oscillation signal with a frequency of f1 outputfrom the first local oscillator 313. When the sum signal with afrequency of fc+fy+f1 out of the mixed signal is passed through the 0.5H delay line 314, then it provides the 0.5 H delayed signal. The thusdelayed signal is then supplied to the second frequency converter 315and band-pass filter 316. The signal with a frequency of fc+fy+f1 thatis supplied to the second frequency converter 315 is mixed here with theoscillation signal with a frequency of f1 output from the first localoscillator 313. Only the difference signal with a frequency offc+fy+f1-f1=fc+fy of the thus mixed signal is taken out by the secondfrequency converter 315 and it is then supplied to the contact b of theswitch 317 as the 0.5 H delayed signal.

The signals respectively supplied to the two contacts a, b of the switch317 are selected alternately at every 1 V according to the controlsignal 318 to be converted into the frame signal 321, and the framesignal 321 is then supplied to the high-pass filter 322. The high-passfilter 322 takes out only the brightness signal component (fy) of theframe signal supplied thereto and also supplies it to the brightnesssignal demodulation circuit 323. In this manner, the brightness signal Ycan be obtained.

On the other hand, after the signal with a frequency of fc+fy suppliedto the low-pass filter 329 has passed through the low-pass filter 329,it becomes only the chroma signal component with a frequency of fc. Thechroma signal component with a frequency of fc is then supplied to thefourth frequency converter 330. In the fourth frequency converter 330,the chroma signal component with a frequency of fc is mixed with theoscillation signal with a frequency of f3 output from the third localoscillator 331. Only the sum component with a frequency of fc+f3 (4˜6.5MHz) of the mixed signal is taken out by the fourth frequency converter330 and is then supplied as a non-delay signal 332 to the contact a ofthe field/frame conversion switch 327.

Also, the signal that is delayed by the 0.5 H delay line 314 istransformed by the band-pass filter 316 into a signal with a frequencyof fc+f1 exclusive of the brightness signal component thereof, and isthen supplied to the third frequency converter 324. The signal thussupplied to the third frequency converter 324 is mixed there with theoscillation signal with a frequency of f2 output from the second localoscillator 325. The difference component with a frequency of fc+f1 -f2(4˜6.5 MHz) of the signals mixed in the third frequency converter 324 isthen extracted and is then supplied as the delayed field signal 326 tothe contact b of the field/frame conversion switch 327.

The respective signals supplied to the contacts a, b of the switch 327are selected alternately at every 1 V according to the control signal328 and are then supplied as the frame signals 333 to the band-passfilter 334. Having passed through the band-pass filter 334, the fieldsignal is transformed into the chroma signal component with a frequencyof fc+f1-f2=fc+f3 (4˜6.5 MHz) and the chroma signal component is thenapplied to the chroma signal demodulation circuit 335 in which thechroma signal can be obtained.

According to the present embodiment, the switching operation for thefield/frame conversion can be performed at the low frequencies and, atthe same time, the chroma demodulation can be executed in the bestcharacteristic portion of the demodulator.

Also, according to the present embodiment, since the 0.5 H time delay ofthe brightness and chroma signals is carried out in the frequencymodulated states thereof before the brightness and chroma signals aredemodulated, it is possible to prevent the occurrence of flickers.

Finally, referring to FIG. 15, there is shown a still further embodimentof a reproducing system in a magnetic recording/reproducing apparatus towhich the invention is applied.

The present embodiment is substantially similar to the embodiment shownin FIG. 14, but it is different from the latter only in that a fieldsignal with a frequency of fc+fy+f1 (for example, 28˜38 MHz) output fromthe first frequency converter 312 is supplied through a band-pass filter339 with a pass bandwidth of fc+f1 (for example, 28˜10.5 MHz) to afourth frequency converter 340, the field signal is mixed with anoscillation signal with an oscillation frequency of f2 (for example, 24MHz) from the second local oscillator 325 in the fourth frequencyconverter 340, the difference component thereof with a frequency offc+f1-f2 (for example, 4˜6.5 MHz) is taken out, and the differencecomponent is supplied to the contact a of the field/frame conversionswitch 327.

The operation of the present embodiment is substantially the same withthe operation of the above-mentioned embodiment shown in FIG. 14, exceptthat the operation of a circuit to obtain a non-delay signal isdifferent to some extent. In other words, in the circuit shown in FIG.14, with regard to the non-delay signal, the signal with a givenbandwidth of fc is taken out from the signal output from the amplifier311 by the low-pass filter 329, and the signal with a given bandwidth offc is converted in frequency by the fourth frequency converter 330 sothat the frequency bandwidth of the signal (fc) can coincide with thatof the delay signal with a frequency of fc+fr-f2. On the other hand, inthe embodiment in FIG. 15, the signal that is converted once into a highfrequency by the first frequency converter 312 is employed as thenon-delay signal and, therefore, in order to carry out the frequencyconversion, the oscillation signal with a frequency of f2 output fromthe second local oscillator 325 can be used, which eliminates the needof one of the local oscillators and also allows the frequency adjustmentto be simplified.

It should be noted here that the above-mentioned demodulation circuits323, 335 are completely identical in structure with the demodulationcircuits shown in FIG. 13 and thus the description thereof is omittedhere.

It should be understood, however, that there is no intention to limitthe invention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

What is claimed is:
 1. A field/frame conversion circuit for a videorecording/reproducing apparatus, comprising:frequency conversion meansfor converting a video field signal from a first frequency bandwidth toa higher second frequency bandwidth; signal delay means for delaying theconverted video field signal by 0.5 of a horizontal scan period; andsignal switching means coupled to receive said delayed video fieldsignal and said converted video field signal for alternately outputtingsaid delayed video field signal and said converted video field signalfor each of a plurality of successive vertical scan periods to form avideo frame signal.
 2. A field/frame conversion circuit as set forth inclaim 1, wherein said video field signal comprises a frequencymultiplexed signal containing at least two frequency modulated signalsof different frequencies.
 3. A field/frame conversion circuit as setforth in claim 2, wherein said at least two frequency modulated signalscomprise a brightness signal and a chroma signal.
 4. A field/frameconversion circuit as set forth in claim 3, wherein said signal delaymeans comprises a glass delay line having a wide frequency bandcharacteristic.